1. Field of the Invention
The present invention relates particularly to a two-man underground utility vehicle for particular use in the coal industry, and which incorporates a hydraulic type, four-wheel drive, skid steer propulsion system controlled by a single lever or "joystick" in the passenger area.
2. Brief Description of the Prior Art
In many mines the areas being worked are narrowly confined; i.e., have low ceilings and side walls closely spaced, and uneven and muddy floors. This has made difficult the use of vehicles to remove miners quickly and safely to and from such areas. Heretofore, no vehicle has been able to function satisfactorily in such conditions and, particularly, to meet the certification requirements of the M.S.H.A. Approval and Certification Center.
Prior art utility vehicles that utilize a single lever or joystick for controlling steering have mechanical linkage to facilitate operation of a four-way valve or a variable volume axial type piston pump to deliver hydraulic pressure to the propulsion means. These configurations create problems in utility vehicles for use in coal mine or underground operations. The vehicles are not sufficiently compact, low in height and easily maneuverable. Mechanical linkage between the joystick and four-way valves or variable volume, axial type piston pumps not only require greater area for installation, but also require considerable maintenance. Further, prior art utility vehicles of this type are not four-wheel drive type but generally utilize drive tracks or are three-wheeled devices which require more power and are subject to getting stuck or "hung up" in soft terrain prevalent in mines.